Engine components and associated auxiliary equipment components may degrade during operation in various ways. For example, an engine cylinder in an engine may start mis-firing due to a worn out ignition plug. A radiator fan (auxiliary equipment) may start wobbling due to an unbalanced fan blade. The performance of a traction motor (auxiliary equipment) may degrade due to an open circuit in a motor coil winding.
One approach to detect engine degradation or auxiliary equipment degradation is to monitor engine speed. Diagnostic routines can monitor whether components of the engine speed rise above a threshold level, and generate diagnostic codes or other indications requesting service, de-rating engine power, shutting down the engine, derating auxiliary equipment power, or shutting down the auxiliary equipment.
However, the inventors herein have recognized that analysis of engine speed is often inadequate to thoroughly diagnose an engine problem or an auxiliary equipment problem. Furthermore, engine speed is often disassociated with certain types of auxiliary equipment (e.g., auxiliary equipment running off of a generator (alternator) connected to the engine such as a radiator fan or a traction motor.